Fluorinated half ester of maleic anhydride polymers for dry 193 nm top antireflective coating application

ABSTRACT

The present invention discloses a composition suitable for use as a top antireflective coating and barrier layer for 193 nm lithography. The inventive composition is soluble in aqueous base solutions and has low refractive index at 193 nm. The inventive composition comprises an aqueous base-soluble polymer having a backbone and a fluorinated half ester moiety. The fluorinated half ester moiety is pendant from the backbone. The present invention also discloses a method of forming a patterned layer on a substrate by using the inventive composition in lithography.

FIELD OF THE INVENTION

The present invention relates to a top anti-reflective coating (“TARC”)material and barrier layer and the use thereof in lithographicprocesses. Particularly, the present invention provides a TARC materialthat is aqueous base-soluble and has a low refractive index (n) at 193nm.

BACKGROUND OF THE INVENTION

In the microelectronics industry as well as in other industriesinvolving construction of microscopic structures (e.g., micromachines,magnetoresistive heads, etc.), there is a continued desire to reduce thesize of structural features. In the microelectronics industry, thedesire is to reduce the size of microelectronic devices and/or toprovide greater amount of circuitry for a given chip size.

Effective lithographic techniques are essential to achieve reduction offeature sizes. Lithography impacts the manufacture of microscopicstructures not only in terms of directly imaging patterns on the desiredsubstrate, but also in terms of making masks typically used in suchimaging. Typical lithographic processes involve formation of a patternedresist layer by patternwise exposing the radiation-sensitive resist toan imaging radiation. The image is subsequently developed by contactingthe exposed resist layer with a base solution, typically an aqueousalkaline developer, to selectively remove portions of the resist layerto obtain the desired pattern. The pattern is subsequently transferredto an underlying material by etching the material in openings of thepatterned resist layer. After the transfer is complete, the remainingresist layer is then removed.

For many lithographic imaging processes, the resolution of the resistimage may be limited by anomalous effects associated with refractiveindex mismatch and undesired reflections of imaging radiation. Toaddress these problems, antireflective coatings are often employedbetween the resist layer and the substrate (bottom antireflectivecoating, also known as BARC) and/or between the resist and theatmosphere in the physical path along which the imaging radiation istransmitted (top antireflective coating, also known as TARC).

For immersion lithography, there are some concerns that certaincomponents in the photoresist may leach out to the immersion medium andchange the performance of the photoresist, or that the immersion mediummay diffuse into the photoresist and affect the acid generation therebyadversely interfering with the chemical amplification mechanism. Toalleviate these problems, a top coat material can be used between theimmersion medium and the resist-coated wafer.

In the case of dry lithographic processes, such as dry 193 nmlithography (not involving an immersion fluid in the radiation exposurestep); the atmosphere would typically be air. In the case of immersionlithography, the atmosphere would typically be water. Water has arefractive index (n) value of around 1.437 at 193 nm. Thus, if futureimmersion lithography requires fluids having refractive index (n) valuesabove 1.6, the atmosphere would likely be hydrocarbons.

The performance of an antireflective coating composition is largelydependent on its optical characteristics at the imaging radiationwavelength of interest. A general discussion regarding typically desiredoptical characteristics of TARCs can be found in U.S. Pat. No.6,274,295. Among the optical parameters of interest are the refractiveindex, the reflectance and the optical density of the TARC.

The antireflective coating composition must also have the desiredphysical and chemical performance characteristics in the context of itsuse in contact directly with, or in close proximity to, the resist layerand in the context of the overall lithographic process (irradiation,development, pattern transfer, etc.). Thus, the TARC should notexcessively interfere with the overall lithographic process. It ishighly desirable that a TARC is removed during the image developmentstep which typically involves dissolution of a portion of the resist inan aqueous alkaline developer solution.

The existing commercial TARC compositions do not possess the combinationof optical properties and physical and chemical performancecharacteristics needed for high resolution 193 nm dry lithography. Forexample, some TARC compositions have a desired refractive index below1.5, but are not soluble in aqueous alkaline developers, thereby causingundesired complication and expense of a separate TARC removal step.Other TARC compositions have a desired refractive index, but adverselyinteract with the resist thus leading to excessive film loss and loss ofcontrast in the resulting resist image or formation of undesired T-topstructures. By “T-top structure”, it is meant that a low solubility thinskin layer formed on top of photoresists to create a “T” shape profileon resist images. Other TARC compositions have desired solubility inaqueous alkaline developer, but have too high a refractive index at 193nm.

Thus, there remains a need for TARC compositions suitable for use in dry193 nm lithographic processes that are aqueous base-soluble and have lowrefractive index on the order of about 1.8 or less at 193 nm. It is alsodesirable that these TARC compositions can be readily prepared fromcommercially available starting materials.

Therefore, there remains another need for TARC and barrier layercompositions suitable for use in immersion 193 nm lithographic processesthat are aqueous base-soluble and have low refractive index on the orderof about 1.8 or less at 193 nm. It is also desirable that these TARCcompositions can be readily prepared from commercially availablestarting materials.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a composition suitablefor use as a top antireflective coating and barrier layer for 193 nmlithography. The composition comprises an aqueous base-soluble polymerhaving a backbone and a fluorinated half ester moiety. The fluorinatedhalf ester moiety is pendant from the backbone. Preferably, thefluorinated half ester moiety comprises the following structure:

wherein R¹ is a fluorine-containing moiety.

The present invention also provides a method of forming a patternedlayer on a substrate. The method comprises: providing a substrate havinga material layer on a surface thereof, depositing a photoresistcomposition on the substrate to form a photoresist layer on thematerial; applying the inventive composition on the photoresist layer toform a top antireflective and barrier layer; pattern-wise exposing thephotoresist layer and the top antireflective and barrier layer to animaging radiation; removing the top antireflective and barrier layer andthe exposed portions of the photoresist layer to form a patternedphotoresist layer on the material layer; and transferring the pattern inthe photoresist layer to the material layer.

DETAILED DESCRIPTION OF THE INVENTION

As stated above, the present invention provides a composition suitablefor use as a top antireflective coating and barrier layer for 193 nmlithography. The inventive composition comprises an aqueous base-solublepolymer having a backbone and a fluorinated half ester moiety. Thefluorinated half ester moiety is pendant from the backbone. The term “afluorinated half ester moiety” as used herein denotes an organic moietyderived from a ring-opening reaction of a cyclic anhydride in thepresence of a fluorinated alcohol. By “a fluorinated alcohol”, it ismeant an alcohol wherein at least a portion of the hydrogen atoms on thecarbonic core are replaced by fluorine atoms. Typically, a fluorinatedhalf ester comprises a carboxylic acid component and a fluorinated estercomponent, where the carboxylic acid component and the fluorinated estercomponent are linked through a covalent bond. While the carboxylic acidcomponent increases the solubility of the inventive polymer in aqueousbase solutions, the fluorinated ester component imparts low refractiveindex (n) to the inventive polymer.

In the present invention, it is preferred that the fluorinated halfester comprises the following structure:

wherein R¹ is a fluorine-containing moiety. It should be understood byone skilled in the art that the fluorinated half ester of formula (I) isattached to the backbone of the aqueous base-soluble polymer as pendantthrough the covalent bonds crossed by the dotted lines. R¹ may be anyorganic group containing multiple fluorine atoms. Preferably, R¹ is afluorinated aliphatic or alicyclic group having 2 to 20 carbon atoms andat least 3 fluorine atoms, which may be optionally substituted byhydroxyl, amino, N-alkyl amino having 1 to 6 carbon atoms, N,N-dialkylamino having 2 to 12 carbon atoms, cyano, cholorine, sulfonate, andsulfonamide. The term “aliphatic group” as used herein denotes anorganic group wherein the carbon atoms are linked in open chains. By “afluorinated aliphatic group”, it is meant an aliphatic group wherein atleast a portion of the hydrogen atoms on the carbonic core are replacedby fluorine atoms. The term “alicyclic group” denotes an organic groupwhere the carbon atoms are linked in ring structures. By “a fluorinatedalicyclic group”, it is meant an alicyclic group wherein at least aportion of the hydrogen atoms on the carbonic core are replaced byfluorine atoms. More preferably, R¹ is a semi- or per-fluorinated alkylgroup having 2 to 20 carbon atoms and at least 3 fluorine atoms, whichmay be optionally substituted by hydroxyl, amino, N-alkyl amino having 1to 6 carbon atoms, N,N-dialkyl amino having 2 to 12 carbon atoms, cyano,cholorine, sulfonate, and sulfonamide. By “semi-fluorinated alkylgroup”, it is meant an alkyl group wherein a portion of the hydrogenatoms on the carbonic core are replaced by fluorine atoms. By“per-fluorinated alkyl group”, it is meant an alkyl group wherein allthe hydrogen atoms on the carbonic core are replaced by fluorine atoms.

In preferred embodiments of the present invention, R¹ is selected fromthe group consisting of —(CF₂)_(p)—CF₃, —(CH₂)—(CF₂)_(q)—CF₃, and—(CH₂)₂—(CF₂)_(r)—CF₃; wherein p is an integer from 1 to 19, q is aninteger from 1 to 18, and r is an integer from 1 to 17. Examples of R¹include, but are not limited to: —(CH₂)₂—(CF₂)—CF₃, —(CH₂)₂—(CF₂)₂—CF₃,—(CH₂)₂—(CF₂)₃—CF₃, —(CH₂)₂—(CF₂)₄—CF₃, —(CH₂)₂—(CF₂)₅—CF₃,—(CH₂)₂—(CF₂)₆—CF₃, —(CH₂)₂—(CF₂)₇—CF₃, —(CH₂)—(CF₂)—CF₃,—(CH₂)—(CF₂)₂—CF₃, —(CH₂)—(CF₂)₃—CF₃, —(CH₂)—(CF₂)₄—CF₃,—(CH₂)—(CF₂)₅—CF₃, and —(CH₂)—(CF₂)₆—CF₃.

In the present invention, it is preferred that the inventive polymer hasan ethylenic backbone. It is more preferred that the aqueousbase-soluble polymer comprises monomeric units selected from the groupconsisting of vinyl, acrylates, methacrylates, and combinations thereof.The backbone of the aqueous base-soluble polymer is preferably free ofunsaturated carbon bonds.

It is also preferred that the inventive polymer further comprisesaromatic moieties. The aromatic moieties are preferably present aspendant groups from the backbone of the inventive polymer. The term “anaromatic moiety” as used herein denotes an organic compoundcharacterized by increased chemical stability resulting from thedelocalization of electrons in one or more rings which typically containmultiple conjugated double bonds. The aromatic moiety of the presentinvention may be carbocyclic or heterocyclic. By “carbocyclic aromaticmoiety”, it is meant an aromatic moiety containing only hydrogen atomsand carbon atoms. By “heterocyclic aromatic moiety”, it is meant anaromatic moiety containing one or more heteroatoms selected fromnitrogen, oxygen, sulfur, or a combination thereof in the aromaticring(s). The aromatic moiety may be monocyclic or polycyclic. The ringsin the polycyclic aromatic moiety may be fused or non-fused.

The aromatic moieties suitable for the present invention include, butare not limited to: fused aromatic moieties, heterocyclic aromaticmoieties, and combinations thereof in substituted or unsubstituted form.Examples of the aromatic moieties include, but are not limited to:naphthalene, thiophene, and combinations thereof in substituted orunsubstituted form. The substituents on the aromatic moieties of thepresent invention include, but are not limited to: alkyl having 1 to 6carbon atoms, alkenyl having 2 to 6 carbon atoms, hydroxyl, amino,N-alkyl amino having 1 to 6 carbon atoms, N,N-dialkyl amino having 2 to12 carbon atoms, cyano, halogen, sulfonate, and sulfonamide.

The aromatic moieties can reduce the refractive index (n) of theinventive polymer as well as increase the absorption of imagingradiation. It is typically, however, preferable to avoid excessiveamount of the aromatic moieties in the inventive polymer.

It is also preferred that the aqueous base-soluble polymer furthercomprises a Si-containing moiety. The Si-containing moiety of thepresent invention may be, for example, Si—Si, Si—C, Si—N, or Si—Omoieties. Preferred Si-containing moieties are the SiO moieties. Morepreferred Si-containing moieties are silsesquioxanes.

In one embodiment of the present invention, the aqueous base-solublepolymer comprises the following structure:

wherein n is an integer of 10 to 500.

The compositions of the present invention may further comprise at leastone solvent which is preferably immiscible with the underlying resistmaterial. Suitable solvents include, but are not limited to: water,1-butanol, methanol, ethanol, 1-propanol, ethylene glycol,1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-propanediol,1-pentanol, 2-pentanol, 3-pentanol, 1-hexanol, 2-hexanol, 3-hexanol,1-heptanol, 2-heptanol, 3-heptanol, 4-heptanol, 2-methyl-1-pentanol,2-methyl-2-pentanol, 2-methyl-3-pentanol, 3-methyl-1-pentanol,3-methyl-2-pentanol, 3-methyl-3-pentanol, 4-methyl-1-pentanol,4-methyl-2-pentanol, 2,4-dimethyl-3-pentanol, 3-ethyl-2-pentanol,1-methylcyclopentanol, 2-methyl-1-hexanol, 2-methyl-2-hexanol,2-methyl-3-hexanol, 3-methyl-3-hexanol, 4-methyl-3-hexanol,5-methyl-1-hexanol, 5-methyl-2-hexanol, 5-methyl-3-hexanol,4-methylcyclohexanol, 1,3-propanediol, octanol, and decane. The amountof solvent in the composition for application to a substrate ispreferably sufficient to achieve a solids content of about 0.5 to about5 wt. %. The compositions may include surfactants or other expedientsknown in the art.

The optical characteristics, solubility, and other physiochemicalproperties of the inventive polymer may be adjusted by either varyingthe ratio among the fluorinated half ester, the aromatic moieties, andthe Si-containing moieties, or introducing functional groups into thefluorinated half ester, the aromatic moieties, and the Si-containingmoieties. If desired, additional co-monomers may be introduced to modifythe dissolution, casting, and other physiochemical properties of theinventive polymer. It is preferred that the inventive polymer is soprepared that the composition of the present invention has a real partof refractive index (n) at 193 nm in a range from about 1.2 to about1.8, with a range from about 1.3 to about 1.5 more preferred. It alsopreferred that the inventive composition has an extinction coefficient(k) at 193 nm in a range from about 0 to about 0.25. The polymers of theinvention preferably have a weight average molecular weight of at leastabout 1,000, more preferably a weight average molecular weight fromabout 1,500 to about 50,000.

The inventive polymer may be prepared by conventional polymerizationtechniques using commercially available and/or easily synthesizedmonomers. For example, the fluorinated half ester can be made bytreating a commercially available cyclic anhydride with a commerciallyfluorinated alcohol. Therefore, the inventive polymer can be readily andeconomically prepared in large scales.

In another aspect of the present invention, the inventive compositionmay be used in a method of forming a patterned material layer on asubstrate. The material layer may be, for example, a ceramic,dielectric, metal or semiconductor layer, such as those used in themanufacture of high performance integrated circuit devices andassociated chip carrier packages. The inventive composition isespecially useful for lithographic processes used in the manufacture ofintegrated circuits on semiconductor substrates. The inventivecomposition may be used in lithographic processes to create patternedmaterial layer structures such as metal wiring lines, holes for contactsor vias, insulation sections (e.g., damascene trenches or shallow trenchisolation), trenches for capacitor structures, ion implanted Sistructures for transistors, etc. as might be used in integrated circuitdevices.

In the inventive method, a photoresist composition is first deposited onthe substrate by known means, to form a photoresist layer on thematerial. The substrate with the photoresist layer may then be baked(post-apply bake, herein after “PAB”) to remove any solvent from thephotoresist composition and improve the coherence of the photoresistlayer. A typical PAB baking temperature is about 80° to about 150° C. Atypical photoresist thickness is about 100 to about 500 nm. Any suitableresist composition may be used, such as the resist composition disclosedin U.S. Pat. Nos. 6,534,239 and 6,635,401 B2, and U.S. patentapplication Ser. No. 10/663,553, filed Sep. 16, 2003, the disclosures ofwhich are incorporated herein by reference.

Next, the inventive composition is applied on the photoresist layer toform a top antireflective and barrier layer. The top antireflective andbarrier layer substantially reduces the substrate reflectivity withrespect to 193 nm radiation. If desired, a bottom antireflective coatingmay be applied to the substrate prior to formation of the resist layer.The inventive composition is preferably applied directly over thephotoresist layer by spin-coating. Any solvent in the inventivecomposition is then removed via a softbaking process. A typicalsoftbaking temperature is about 90° C. A typical softbaking time isabout 90 seconds. The thickness of the top antireflective and barrierlayer is typically in the range from about 20 to about 60 nm.

The photoresist layer and the top antireflective and barrier layer isthen exposed to an appropriate radiation source through a patternedmask. In one exemplary embodiment, the imaging radiation is 193 nmradiation. For 193 nm UV radiation, the total exposure energy ispreferably about 100 millijoules/cm² or less, more preferably about 50millijoules/cm² or less (e.g. 15-30 millijoules/cm²). After the desiredpatternwise exposure, the resist layer is typically baked to furthercomplete the acid-catalyzed reaction and to enhance the contrast of theexposed pattern. The post-exposure bake is preferably conducted at about60° to about 175° C., more preferably about 90° to about 160° C. Thepost-exposure bake is preferably conducted for about 30 seconds to about5 minutes.

The top antireflective and barrier layer and the exposed photoresistlayer are then contacted with an aqueous base developer, such as 0.263 Ntetramethyl ammonium hydroxide, thereby removing the top antireflectiveand barrier layer and the exposed portions of the photoresist layer fromthe coated substrate. As is known to those skilled in the art, contactwith a developer forms a patterned photoresist layer on the materiallayer.

The pattern in the photoresist layer may then be transferred to thematerial layer on the underlying substrate. Typically, the transfer isachieved by reactive ion etching or some other etching technique. Themethod of the invention may be used to create patterned material layerstructures such as metal wiring lines, holes for contacts or vias,insulation sections (e.g., damascene trenches or shallow trenchisolation), trenches for capacitor structures, etc. as might be used inthe design of integrated circuit devices. Alternatively, the pattern maybe transferred by ion implantation to form a pattern of ion implantedmaterial.

The processes to make these (ceramic, dielectric, metal orsemiconductor) features generally involve providing a material layer orsection of the substrate to be patterned, applying a layer ofphotoresist over the material layer or section, applying a top coatlayer on the layer of photoresist, pattern-wise exposing the top coatand photoresist layers to radiation, post-exposure baking the exposedresist, developing the pattern by contacting the exposed top coat andphotoresist with a developer, etching the layer(s) underlying thephotoresist layer at spaces in the pattern whereby a patterned materiallayer or substrate is formed, and removing any remaining photoresistfrom the substrate. In some instances, a hard mask may be used below thephotoresist layer to facilitate transfer of the pattern to a furtherunderlying material layer or section. It should be understood that theinvention is not limited to any specific lithography technique or devicestructure.

The following non-limiting examples are provided to further illustratethe present invention. Because the examples are provided forillustrative purposes only, the invention embodied therein should not belimited thereto.

EXAMPLE 1

Synthesis and Optical Property Characterization of a Fluorinated HalfEster of Polyethylenemaleic Anhydride.

Polyethylenemaleic anhydride obtained from Aldrich was dissolved in3,3,4,4,5,5,6,6,6-nanofluoro-1-hexanol and was heated up to 135° C.overnight. The obtained polymer solution was spin-coated on a siliconwafer and then baked on a hot plate at 110° C. for 60 seconds. Then nand k values were measured with a VB-250 VASE Ellipsometer manufacturedby J.A. Woollam Co. Inc. The measured optical properties of the film forthis fluorinated half ester exhibited an n value of 1.464 and a k valueof 0.0006598 at 193 nm.

EXAMPLE 2

Optical Properties of Some Other Polymers and Compound ComprisingFluorinated Half Ester Synthesized.

One silicon containing compound and two selected polymers combiningdifferent amounts of various monomers were synthesized, and thenconverted to their corresponding fluorinated half esters with the methoddescribed in Example 1 except the reaction time was around 3 to 4 hoursinstead of overnight. The materials obtained were then measured with themethod described in Example 1, and exhibited optical properties with ann value of below 1.6 at 193 nm as shown below:

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe invention. It is therefore intended that the present invention notbe limited to the exact forms and details described and illustrated butfall within the scope of the appended claims.

1. A method of forming a patterned layer on a substrate, the methodcomprising: providing a substrate having a material layer on a surfacethereof; depositing a photoresist composition on the substrate to form aphotoresist layer on the material; applying a composition on thephotoresist layer to form a top antireflective and barrier layer, saidcomposition comprising an aqueous base-soluble polymer having a backboneand a fluorinated half ester moiety, wherein the fluorinated half estermoiety are pendant from the backbone; pattern-wise exposing thephotoresist layer and the top antireflective and barrier layer to animaging radiation; removing the top antireflective and barrier layer andthe exposed portions of the photoresist layer to form a patternedphotoresist layer on the material layer; and transferring the pattern inthe photoresist layer to the material layer.
 2. The method of claim 1,wherein the top antireflective and barrier layer and the exposedportions of the photoresist layer are removed by contacting the topantireflective and barrier layer and the photoresist layer with anaqueous alkaline developer.
 3. The method of claim 1, wherein thematerial is selected from the group consisting of ceramic, dieletric,metal, and semiconductor layer.
 4. The method of claim 1, wherein thepattern in the photoresist layer is transferred to the material layer byremoving portions of the material layer not covered by the patternedphotoresist layer.
 5. The method of claim 4, wherein portions of thematerial layer not covered by the patterned photoresist layer areremoved by using reactive ion etching or ion implanting.